fix: do not require a local image for k3s deploys

Kubernetes pulls the app image itself, so a k3s host is free to reap its local copy while the workload keeps running, which the `registry` plugin already does on its own. Deploys, restarts, `dokku run`, and in-cluster cron no longer assert that the image is present locally, falling back to the metadata recorded in the app's current Helm release. A `ps:restart` naming a single process type now rolls only that process type's pods rather than silently redeploying every one. Apps with an `app.json` postdeploy task still require the image locally, as that task runs on the Dokku host.

docs/development/plugin-triggers.md

@@ -2562,16 +2562,16 @@ source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 > The scheduler plugin trigger apis are under development and may change
 > between minor releases until the 1.0 release.
 
-- Description: Allows you to run scheduler commands when an app is deployed
+- Description: Allows you to run scheduler commands when an app is deployed. `$PROCESS_TYPE` is empty for a normal deploy and set when a single process type is targeted, as by `dokku ps:restart <app> <process-type>`, in which case only that process type should be redeployed.
 - Invoked by: `dokku deploy`
-- Arguments: `$DOKKU_SCHEDULER $APP $IMAGE_TAG`
+- Arguments: `$DOKKU_SCHEDULER $APP $IMAGE_TAG $PROCESS_TYPE`
 - Example:
 
 ```shell
 #!/usr/bin/env bash
 
 set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
-DOKKU_SCHEDULER="$1"; APP="$2"; IMAGE_TAG="$3";
+DOKKU_SCHEDULER="$1"; APP="$2"; IMAGE_TAG="$3"; PROCESS_TYPE="$4";
 
 # TODO
 ```